JP2017034930A - Electric vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To generate a brake force in the case when a friction brake force cannot be generated during regenerative limitation.SOLUTION: An MG-ECU has a limitation value 222 set according to a state of a battery and a release value 223 capable of generating a larger brake force than the limitation value 222 as regenerative limitation values. In a state of limiting regenerative brake, the MG-ECU generates a friction brake force 231 based on a difference F1 between the release value 223 and a required driving force 221 of a driver. In a state of limiting regeneration, if the friction brake force 231 is also limited, the MG-ECU switches the regenerative limitation value from the release value to the limitation value and requires a motor generator to generate regenerative brake on the basis of the limitation value.SELECTED DRAWING: Figure 3

Description

  The present embodiment relates to an electric vehicle provided with a motor for traveling.

  Patent Document 1 discloses a technique for switching from a regenerative braking force to a friction braking force when a battery that stores regenerated electric power or the like is fully charged in an electric vehicle.

JP-A-10-271605

  For example, as in the technique disclosed in Patent Document 1, in a vehicle such as an electric vehicle, when a battery for storing regenerated electric power is fully charged, the regenerative braking force is switched to the friction braking force. .

  In particular, in an electric vehicle as well, a braking force equivalent to an engine brake can be realized by a regenerative braking force in order to realize braking like an engine brake of a general gasoline vehicle or diesel vehicle. In this case, when the amount of charge of the battery approaches a reference value that is the limit of charging, the regenerative braking force is gradually decreased while the friction braking force is gradually increased to realize a braking force equivalent to the engine brake. Can be considered to smoothly shift from regenerative braking force to friction braking force. In addition to the braking force required by the driver, if the regenerative braking force is limited to charge the battery or protect the battery and the braking force is insufficient, a friction braking force is generated. Is also possible.

By the way, the technique described in Patent Document 1 switches from regenerative braking to friction braking when the battery is regeneratively restricted due to full charge or the like. Conventionally, at the time of regeneration restriction, the deficiency with respect to the driving force required by the driver (required driving force) was compensated by friction braking force, but failure due to friction braking force or brake parts (brake pads and If the temperature of the rotor) increases, the friction braking force cannot be generated.
However, Patent Document 1 does not describe how to generate the braking force when the frictional braking force cannot be generated during the regeneration limit.

  Therefore, an object of the present invention is to generate a braking force when the friction braking force cannot be generated during the regeneration limit.

  The invention according to claim 1 of the present invention that solves the above-described problems includes a regenerative braking force generator that generates a regenerative braking force in the vehicle, a battery that stores electric power regenerated by the regenerative braking force, and friction to the vehicle. A friction braking force generation unit that generates a braking force; and a control unit that controls the regenerative braking force and the generation of the friction braking force, wherein the control unit uses the battery as a limiting threshold value of the regenerative braking force. And a second regenerative restriction threshold that can generate a braking force larger than the first regenerative restriction, and regenerative braking is restricted. In the state, the friction braking force is generated based on the difference between the second regenerative restriction threshold and the driver's requested driving force, and the friction braking force is further restricted in the regenerative braking state. , The limit threshold is the second threshold Switch to the first regeneration limit threshold from the raw limit threshold, an electric vehicle, characterized in that requests the regenerative braking force generating unit so as to generate the regenerative braking on the basis of the first regenerative limit threshold.

  According to the first aspect of the present invention, the braking force can be generated even when the friction braking is restricted during the regeneration restriction.

  The invention according to claim 2 is the electric vehicle according to claim 1, wherein the control unit performs the second operation from the first regeneration limit threshold when the driver performs an acceleration operation. It is characterized by switching to the regeneration limit threshold value.

  According to the second aspect of the present invention, it is possible to prevent the occurrence of a shock due to the sudden disappearance of the braking force corresponding to the frictional braking by switching to the state where the frictional braking is not used while the frictional braking is being performed. Can do.

  The invention according to claim 3 is the electric vehicle according to claim 1 or 2, wherein the first regenerative restriction threshold is the regenerative braking when the battery is in a regenerative braking state. It is based on the regenerative braking force which a power generation part can output.

  According to the third aspect of the present invention, a limited regenerative braking force can be generated even in a state where friction braking is limited.

  Moreover, the invention according to claim 4 is the electric vehicle according to any one of claims 1 to 3, wherein the first regenerative restriction threshold value is that the battery is in a non-regenerative braking state. Sometimes, the regenerative braking force generator is based on a regenerative braking force that can be output.

  According to the fourth aspect of the present invention, it is possible to output all of the requested braking force in a state where friction braking is not limited.

  The invention according to claim 5 is the electric vehicle according to any one of claims 1 to 4, wherein the control unit is generated based on the first regeneration restriction threshold value. Regenerative braking is output smoothly.

  According to the invention which concerns on Claim 5, the discontinuity of the braking force which arises when a required braking force is restrict | limited by the 1st regeneration restriction threshold value can be eliminated. Thereby, a driver's uncomfortable feeling can be eliminated and feeling can be improved.

  The invention according to claim 6 is the electric vehicle according to any one of claims 1 to 5, wherein the control unit performs the friction braking force when the friction braking is limited. Is gradually reduced.

  According to the sixth aspect of the present invention, it is possible to prevent a sudden decrease in braking force.

  According to the present invention, it is possible to generate a braking force when the frictional braking force cannot be generated during the regeneration limit.

It is a principal part system diagram of the vehicle concerning this embodiment. It is a block diagram which shows the system configuration | structure of the control system of a vehicle. It is a figure which shows the timing chart of operation | movement in MG-ECU and ESB-ECU which concern on this embodiment, (a) And (d) shows the operation | movement in ESB-ECU, (b) And (c) is MG-ECU. The operation in is shown. It is a figure which shows the time change of the request | requirement driving force and regeneration limit value in a comparative example. It is a block diagram which shows the structure of MG-ECU and ESB-ECU. It is a flowchart which shows the operation | movement procedure of the action | operation judgment part of ESB-ECU. It is a flowchart which shows the operation | movement procedure of MG-ECU which concerns on this embodiment. It is a flowchart which shows the operation | movement procedure of the hydraulic pressure control part of ESB-ECU.

  Next, modes for carrying out the present invention (referred to as “embodiments”) will be described in detail with reference to the drawings as appropriate.

[overall structure]
FIG. 1 is a system diagram of a main part of a vehicle according to the present embodiment.
The vehicle 100 is, for example, an electric vehicle, and includes a pair of left and right front wheels 2aR and 2aL provided on the front side of the vehicle 100, and a pair of left and right rear wheels 2bR and 2bL provided on the rear side of the vehicle 100. . A motor generator (MG) 3 is connected to a front wheel axle 4 connected to the left and right front wheels 2aR, 2aL by a torque transmission mechanism. The vehicle 100 may be four-wheel drive, rear-wheel drive, or may be configured as a hybrid vehicle including the motor / generator 3. The differential mechanism provided on the front wheel axle 4 is not shown.

  The motor / generator 3 serves both as an electric motor for driving the vehicle 100 and a generator for regeneration. A battery 5 as a secondary battery supplies power to the motor / generator 3 by an inverter 6 as a power source of the motor / generator 3. Further, when the vehicle 100 is decelerated, the motor / generator 3 converts the deceleration energy into electric power, and the battery 5 stores the regenerated generated electric power. During this regeneration, the motor / generator 3 generates a regenerative braking force. That is, a regenerative braking force generator is realized by the motor / generator 3 and the like.

Further, the battery 5 is provided with a charge amount detection sensor 8 (voltage sensor and / or current sensor) for detecting a charge amount (SOC: State Of Charge) of the battery 5. Incidentally, although control of the battery 5 is performed by the battery ECU, the battery ECU is omitted in the present embodiment.
An MG-ECU 7 (Management-Electronic Control Unit: control unit) 7 is a device that includes a microcomputer and controls each unit intensively (details will be described later).
In addition, the ESB-ECU 13 (Electric Servo Brake-Electronic Control Unit: control unit) sends a control signal via a signal line in accordance with the required friction braking force output from the MG-ECU 7 so that the friction braking device 10 is not illustrated. The electric motor is controlled (details will be described later).

  The friction braking device 10 is a friction braking force generator. That is, each wheel 2aR, 2aL, 2aR, 2aL is connected to each wheel cylinder of the disc brake mechanism 30a-30d, and the wheel cylinder is driven by hydraulic pressure, and the brake pad is pressed against the brake rotor to generate friction braking force. It is a device for generating.

  Various devices can be applied as the friction braking device 10 as long as they are braking devices for generating a friction braking force. For example, a so-called by-wire brake system can be applied. The by-wire brake system includes an electric motor, and drives the disc brake mechanisms 30a to 30d of the wheels 2aR, 2aL, 2bR, and 2bL by operating the hydraulic mechanism according to the control of the electric motor. , A device that applies a friction braking force to the wheels 2aR, 2aL, 2bR, 2bL.

[System configuration of control system]
FIG. 2 is a block diagram showing a system configuration of a vehicle control system.
The MG-ECU 7 includes a brake pedal stroke sensor 21 that detects an operation amount of a brake pedal, an accelerator opening sensor 22 that detects an accelerator opening, and the charge amount detection sensor 8 described above via a predetermined interface. Connected by signal lines. Further, the motor / generator 3, the inverter 6, and the battery 5 are connected to the MG-ECU 7 by a signal line through a predetermined interface. Further, the MG-ECU 7 receives a detection signal (wheel speed signal) of the wheel speed sensor 11. The wheel speed sensor 11 is a sensor that detects the rotational speed of the wheel. The wheel speed signal is a pulse wave that generates a predetermined number of pulses each time the wheel rotates once. The MG-ECU 7 calculates the vehicle speed of the vehicle 100 based on the wheel speed signal input from the wheel speed sensor 11. Therefore, the wheel speed sensor 11 is a vehicle speed sensor that detects the vehicle speed.

The ESB-ECU 13 is connected to a pad temperature sensor 12 for measuring the temperature of a brake pad provided in each wheel 2aR, 2aL, 2aR, 2aL via a predetermined interface via a signal line. Furthermore, the MG-ECU 7 and the friction braking device 10 are connected to the ESB-ECU 13 by signal lines.
Detailed descriptions of the MG-ECU 7 and the ESB-ECU 13 will be described later.

[Timing chart]
FIG. 3 is a diagram showing a timing chart of operations in the MG-ECU and the ESB-ECU according to the present embodiment. FIGS. 3A and 3D show the operation in the ESB-ECU 13, and FIGS. 3B and 3C show the operation in the MG-ECU 7. FIG.
First, reference numeral 201 in FIG. 3A indicates a change in the temperature of the brake pad (hereinafter referred to as pad temperature) over time. Reference numeral 202 denotes a friction braking control interruption flag transmitted from the ESB-ECU 13 to the MG-ECU 7, and is in an ON state or an OFF state.

Moreover, the code | symbol 211 in FIG.3 (b) shows ON / OFF of the friction braking control in MG-ECU7.
In FIG. 3C, reference numeral 221 indicates a transient process (smoothed) of the required driving force, reference numeral 222 indicates a limit value of the regeneration limit value, and reference numeral 223 indicates a regeneration limit value. Indicates the release value.
In the present embodiment, the driving force includes a braking force. That is, of the driving forces, the driving force in the traveling direction of the vehicle 100 (referred to as + direction as appropriate) is referred to as “driving force”, and the driving force in the direction opposite to the traveling direction (referred to as − direction as appropriate) is “controlled”. "Power". Therefore, the required driving force 221 includes the required braking force. In addition, when it is clearly a braking force, it is described as “braking force”.

A regenerative limit value limit value (first regenerative limit threshold value) 222, which is a regenerative braking force limit threshold value, is set according to the state of the battery 5, and limits the motor torque in the motor / generator 3 and the power storage of the battery 5. This is a limit value when power is limited. That is, the limit value 222 is a regenerative braking force that can be output by the motor / generator 3 when the regenerative restriction is performed. In this way, it is possible to generate a limited regenerative braking force even in a state where friction braking is limited. Note that the limit value 222 is somewhat at the expense of the life of the battery 5 even in a fully charged state. However, it may be a value that can be regenerated.

  The regenerative limit value release value (second regeneration limit threshold value) 223 is not limited by the motor torque in the motor / generator 3 or the stored power in the battery 5, and can be output according to the specifications of the battery 5. This is a limit value. That is, the release value 223 is a regenerative braking force that can be output by the motor / generator 3 when regenerative restriction is not performed (during non-regenerative restriction), and a braking force larger than the limit value 222 can be generated. . By doing so, it is possible to output all of the requested braking force in a state where friction braking is not limited.

Reference numeral 224 indicates an accelerator work. Reference numeral 225 will be described later.
Reference numeral 231 in FIG. 3D indicates the friction braking force output from the friction braking device 10.
Incidentally, it is assumed that the battery 8 is determined to be in the regeneration limit state based on the SOC detected based on the charge amount detection sensor 8 (see FIG. 1).

(Time t0 to t1)
In this section, the driver turns off the accelerator pedal and is in a regenerative braking state (corresponding to the engine braking state of a gasoline engine), but because the regenerative restriction is in effect, the friction braking force 231 supplements the insufficient braking force. doing.
In this section, the regeneration limit value is set to the release value 223. Therefore, the MG-ECU 7 requests a braking force up to the release value 223, but since regeneration is being restricted, the MG-ECU 7 requests the motor generator 3 to apply a braking force up to the release value 223 as the braking force due to regeneration. And MG-ECU7 requests | requires the braking force of the difference F1 of the request | requirement braking force 221 and the release value 223 as a friction braking force. The ESB-ECU 13 outputs the friction braking force 231 requested from the MG-ECU 7.

(Time t1 to t2)
At time t1, when the pad temperature 201 exceeds the first threshold value Th1 to stop the friction braking control (limit friction braking), the ESB-ECU 13 raises the friction braking control interruption flag 202 (from the OFF state to the ON state). ).
The MG-ECU 7 that has received the interruption flag 201 in the ON state requests a braking force up to the release value 223 as shown in FIG. 3C, but the ESB-ECU 13 By gradually releasing the hydraulic pressure, the friction braking force 231 is gradually decreased as shown in FIG. By doing so, it is possible to prevent a sudden decrease in braking force.

(Time t2 to t3)
At time t2, the friction braking force 213 in FIG. 3D becomes 0, but the MG-ECU 7 keeps the friction braking state 211 in the ON state and keeps the regeneration limit value at the release value 223.

(Time t3 to t4)
At time t3, when the driver depresses the accelerator pedal (acceleration operation) and the required driving force 224 becomes the + side (traveling direction), the MG-ECU 7 sets the friction braking state 211 to the OFF state and sets the regeneration limit value to the limit value Switch to 222. The depression of the accelerator pedal is determined by the MG-ECU 7 based on an input from the accelerator opening sensor 22 (see FIG. 1) or the like. Thereafter, the braking force that can be requested by the MG-ECU 7 is a value up to the limit value 222. In this way, it is possible to generate a braking force even when friction braking is limited during regeneration limitation.

  Thus, the MG-ECU 7 does not immediately switch the regeneration limit value even when the friction braking control is in the OFF state. Then, the MG-ECU 7 turns off the friction braking state 211 for the first time and switches the regeneration limit value when the driver depresses the accelerator pedal and the required driving force 224 becomes the + side (traveling direction). In this way, friction braking is performed by switching the regeneration limit value in a state where the braking force is not required (the accelerator pedal is depressed and the required driving force 224 is on the + side (traveling direction)). By switching to a state in which friction braking is not used while the braking is being performed, it is possible to prevent the occurrence of a shock due to sudden and sudden disappearance of the braking force for friction braking.

(Time t4 to t6)
At time t4, when the driver turns off the accelerator pedal again, a regenerative braking state (equivalent to an engine brake of a gasoline engine) is established. At this time, the MG-ECU 7 normally requests the braking force indicated by the broken line 225, but the regeneration limit value is limited to the limit value 222 as described above. As described above, the MG-ECU 7 transiently processes (smooths) and outputs the required driving force 221 (solid line) up to the limit value 222. By doing so, it is possible to eliminate the discontinuity of the braking force that occurs when the required braking force is limited by the first regeneration limit threshold. Thereby, a driver's uncomfortable feeling can be eliminated and feeling can be improved.

  At time t5, as shown in FIG. 3A, the pad temperature 201 falls to a temperature Th2 at which friction braking control is possible, and the ESB-ECU 13 turns off the interruption flag for friction braking control. However, the MG-ECU 7 keeps the friction braking state ON as shown in FIG. 3B and keeps the regeneration limit value at the limit value 222 as well.

(Time t6 to t7)
At time t6, when the driver depresses the accelerator pedal and the required driving force 224 becomes the + side (traveling direction), the MG-ECU 7 sets the friction braking state 211 to the ON state as shown in FIG. As shown in FIG. 3 (c), the regeneration limit value is switched to the release value 223. Thereafter, the braking force that can be requested by the MG-ECU 7 becomes the braking force up to the release value 223, and the braking force can be supplemented by the friction braking force 231.

  Thus, the MG-ECU 7 does not immediately switch the regeneration limit value even when the friction braking control is in the ON state. Then, the MG-ECU 7 turns on the friction braking state 211 for the first time when the driver depresses the accelerator pedal and the required driving force 224 becomes the + side (traveling direction), and switches the regeneration limit value. In this way, the friction is reduced by switching the regenerative limit value in a state where the regenerative braking force is not required (the accelerator pedal is depressed and the required driving force 224 is on the + side (traveling direction)). By switching to a state where friction braking is not used while braking is being performed, it is possible to prevent the occurrence of a shock due to sudden loss of braking force for friction braking.

(From time t7)
At time t7, the driver turns off the accelerator pedal again to enter a regenerative braking state (equivalent to an engine brake of a gasoline engine). As shown in FIG. 3C, until the time t8, the required braking force 221 is equal to or greater than the limit value 222, and thus no supplementation with the friction braking force 231 is necessary.

  When the required braking force 221 becomes equal to or less than the limit value 222 at time t8, the ESB-ECU 13 outputs a friction braking force 231 corresponding to the difference between the required braking force 221 and the limit value 222.

[Comparative example]
FIG. 4 is a diagram illustrating a time change between the required driving force and the regeneration limit value in the comparative example.
FIG. 4 corresponds to FIG. 3C, and the times other than the time t11 are the same as those in FIG. 3C, and thus the description thereof is omitted here.
Further, reference numerals 222 to 224 are the same as those in FIG.
As shown in FIG. 4, the required driving force 251 in the comparative example changes discontinuously as indicated by a broken-line circle at time t4 and time t11. As a result, the driver feels uncomfortable.

  In the present embodiment, as shown in the section from time t4 to t6 in FIG. 3C, the transient processing is performed on the required driving force 221 even in the section where only the limit value 222 can be output. Discontinuity can be eliminated and the driver's discomfort can be eliminated.

[Configuration of MG-ECU 7 and ESB-ECU 13]
FIG. 5 is a block diagram showing configurations of the MG-ECU and the ESB-ECU.
The processing performed by each unit shown in FIG. 5 will be described later.
(Configuration of MG-ECU 7)
The MG-ECU 7 includes a switching unit 301, a first restriction processing unit 302, a transient processing unit 303, a second restriction processing unit 304, and a friction braking control unit 305.
The switching unit 301 switches the regeneration limit value to the limit value 222 (FIG. 3C) or the release value 223 (FIG. 3C) based on the interruption flag sent from the ESB-ECU 13 and the requested driving force. .
The first limit processing unit 302 performs a limit process on the required driving force with the current regeneration limit value switched by the switching unit 301.

The transient processing unit 303 performs a transient process on the output result (restricted required driving force) of the first limiting processing unit 302 so that the required driving force changes smoothly over time.
The second restriction processing unit 304 restricts the output result of the transient processing unit 303 (required driving force after transient processing) by the limit value 222. If the current regeneration limit value (regeneration limit value after switching) is the release value 222, the output of the second restriction processing unit 304 is the same as the output of the transient processing unit 303. If the current regeneration limit value is the limit value 223, the output of the second limit processing unit 304 is that in which the requested driving force is limited by the release value 223. The second restriction processing unit 304 outputs its own output result as the required regenerative braking force to the motor / generator 3 and also to the friction braking control unit 305.

  The friction braking control unit 305 calculates a difference between the output of the transient processing unit 303 and the output of the second restriction processing unit 304, and outputs the calculated difference value to the ESB-ECU 13 as a required friction braking force. At this time, if the current regeneration limit value (regeneration limit value after switching) is the limit value 222, as described above, the output of the second limit processing unit 304 and the output of the transient processing unit 303 have the same value. Therefore, the friction braking control unit 305 outputs 0 as the required friction braking force. That is, MG-ECU 7 does not generate a friction braking force if the current regeneration limit value is limit value 222. If the current regenerative limit value is the release value 223, a difference value between the output of the transient processing unit 303 and the output of the limit value 222 is output as the required friction braking force.

(Configuration of ESB-ECU 13)
The ESB-ECU 13 includes an operation determination unit 311 and a hydraulic pressure control unit 312.
Based on the pad temperature input from the pad temperature sensor 12, the operation determination unit 311 outputs ON / OFF of the friction braking control interruption flag to the MG-ECU 7 and the hydraulic pressure control unit 312.
The hydraulic pressure control unit 312 controls the hydraulic pressure of each part in the friction braking device 10 according to the required friction braking force output from the friction braking control unit 305 of the MG-ECU 7 to generate the friction braking force. Further, the hydraulic pressure control unit 312 performs a process of gradually releasing the hydraulic pressure of the friction braking device 10 according to the ON / OFF state of the interruption flag output by the operation determination unit 311.

[flowchart]
(Operation of Operation Determination Unit 311 of ESB-ECU 13)
FIG. 6 is a flowchart showing an operation procedure of the operation determination unit of the ESB-ECU. Reference is made to FIGS. 3 and 5 as appropriate. Incidentally, in FIGS. 6 to 8, it is assumed that the battery 8 is determined to be in the regeneration limited state based on the SOC detected based on the charge amount detection sensor 8 (see FIG. 1).
First, the operation determination unit 311 receives an input of the pad temperature 201 from the pad temperature sensor 12 (FIG. 1) (S101).
Then, the operation determination unit 311 determines whether or not the pad temperature is equal to or higher than a threshold value Th1 at which the frictional braking control is interrupted (S102).
As a result of step S102, when the pad temperature is equal to or higher than the threshold Th1 (S102 → Yes), the operation determination unit 311 transmits a friction braking control interruption flag ON to the MG-ECU 7 (S103). The processing in step S103 corresponds to time t1 in FIG. In the initial state (when the ignition is ON), the interruption flag is OFF.

When the pad temperature is lower than the threshold value Th1 as a result of step S102 (S102 → No), the operation determining unit 311 determines whether the pad temperature is equal to or lower than the threshold value Th2 for resuming the frictional braking control (S111). .
As a result of step S111, when the pad temperature is lower than the threshold value Th2 (S111 → Yes), the operation determination unit 311 transmits an interruption flag OFF to the MG-ECU 7 and the hydraulic pressure control unit 312 (S112). . The processing in step S103 corresponds to time t5 in FIG.
As a result of step S111, when the pad temperature is higher than the threshold Th2 (S111 → No), the operation determination unit 311 maintains the current state of the interruption flag (S121).

(Operation of MG-ECU 7)
FIG. 7 is a flowchart showing an operation procedure of the MG-ECU according to the present embodiment. Reference is made to FIGS. 3 and 5 as appropriate.
First, the switching unit 301 determines whether or not the state of the interruption flag transmitted from the operation determination unit 311 of the ESB-ECU 13 is the same as the friction braking state (S201). For example, when the interruption flag 202 and the friction braking state 211 are both ON as in the interval from time t1 to t3 in FIG. 2, the switching unit 301 has the same interruption flag state and friction braking state. It is determined that Further, when both the interruption flag 202 and the friction braking state 211 are OFF as in the section from time t5 to t6, the switching unit 301 has the same interruption flag state and friction braking state state. judge. When one of the interruption flag 202 and the frictional braking state 211 is ON and the other is OFF as at times t0 to t1, t3 to t5, and t6 to in FIG. It is determined that the friction braking state is not the same.

  As a result of step S201, when the state of the interruption flag is not the same as the state of the friction braking state (S201 → No), the MG-ECU 7 advances the process to step S221. That is, the MG-ECU 7 calculates and outputs the regenerative braking force and the friction braking force using the current regenerative limit value.

As a result of step S201, when the state of the interruption flag is the same as the state of the friction braking state (S201 → Yes), the switching unit 301 determines whether the required driving force on the drive (Dr) side has changed to the + side. Is determined (S202). “The required driving force on the drive (Dr) side has changed to the + side” is when the driver depresses the accelerator pedal (when an acceleration operation is performed).
As a result of step S202, when the required driving force on the drive side changes to the + side (S202 → Yes), the switching unit 301 switches the friction braking state (S211) and switches the regeneration limit value (S212). These processes correspond to the time t3 and the time t6 in FIGS. 3B and 3C.
After step S213, the MG-ECU 7 advances the process to step S221.
As a result of step S202, when the requested driving force on the drive side has not changed to the + side (S202 → No), the MG-ECU 7 advances the process to step S221.

  In step S <b> 221, the first restriction processing unit 302 performs a first restriction process in which the requested driving force is restricted with the current regeneration restriction value switched by the switching unit 301.

Next, the transient processing unit 303 performs a transient process on the output result of the first restriction processing unit 302 (S222) so that the required driving force changes smoothly with time.
Subsequently, the second restriction processing unit 304 performs second restriction processing for restricting the output result of the transient processing unit 303 with the restriction value 222 (S223). The second restriction processing unit 304 outputs its own output result as the required regenerative braking force to the motor / generator 3 and also to the friction braking control unit 305.

  Then, the friction braking control unit 305 calculates the difference between the output of the transient processing unit 303 and the output of the second restriction processing unit 304, and outputs the calculated difference value to the ESB-ECU 13 as the required friction braking force. Processing is performed (S224). After step S224, the MG-ECU 7 returns the process to step S201.

(Operation of Hydraulic Pressure Control Unit 312 of ESB-ECU 13)
FIG. 8 is a flowchart showing an operation procedure of the hydraulic pressure control unit of the ESB-ECU. Reference is made to FIGS. 3 and 5 as appropriate.
First, the hydraulic control unit 312 determines whether or not the current friction braking control interruption flag is in an ON state (S301).
If the interruption flag is not currently ON as a result of step S301 (S301 → No), the hydraulic pressure control unit 312 performs hydraulic pressure control according to the required friction braking force sent from the MG-ECU 7 (S311). After step S311, the hydraulic pressure control unit 312 returns the process to step S301.
As a result of step S301, when the interruption flag is currently ON (S301 → Yes), the hydraulic pressure control unit 312 determines whether or not the currently output friction braking force is greater than 0 (S302).

As a result of step S302, when the friction braking force currently output is 0 (S302 → No), the hydraulic pressure control unit 312 returns the process to step S301. That is, the hydraulic pressure control unit 312 maintains the state of zero friction braking force.
As a result of step S302, if the currently output friction braking force is greater than 0 (S302 → Yes), the hydraulic pressure control unit 312 releases the hydraulic pressure of the friction braking device 10 (S303). At this time, the hydraulic pressure to be extracted is very small. Thereby, the friction braking force gradually decreases. After step S303, the hydraulic pressure control unit 312 returns the process to step S301. Note that the processing in step S303 corresponds to times t1 to t2 in FIG.

According to this embodiment, when friction braking is limited, the state where friction braking is limited by switching the regenerative limit value from the limit value to the release value and generating a regenerative braking force corresponding to the limit value. However, a braking force can be generated.
In addition, when the driver performs an acceleration operation by depressing the accelerator pedal, by switching the regenerative limit value, the friction brake is switched to a state in which it is not used while the friction brake is being performed. Further, it is possible to prevent the occurrence of shock due to the sudden disappearance of the braking force for friction braking.
Furthermore, according to the present embodiment, by performing a transient process in which a value obtained by limiting the required driving force with the limit value is smoothed and then output, it occurs when the required braking force is limited by the first regeneration limit threshold value. The discontinuity of braking force can be eliminated. Thereby, a driver's uncomfortable feeling can be eliminated and feeling can be improved.

  In the present embodiment, the case where the temperature of the brake pad becomes equal to or higher than the predetermined temperature has been described. However, the present invention can also be applied to a case where friction braking is insufficient due to a servo failure or the like.

2aR, 2aL Front wheel (wheel)
2bR, 2bL Rear wheel (wheel)
3 Motor generator (regenerative braking force generator)
5 Battery 6 Inverter 7 MG-ECU (Control Unit)
10 Friction braking device (friction braking generator)
11 Wheel speed sensor 12 Pad temperature sensor 13 ESB-ECU (control unit)
100 vehicle (electric vehicle)
221 Required driving force 222 Limit value (first regeneration limit threshold, limit threshold)
223 Release value (second regeneration limit threshold, limit threshold)
224 Accelerator work 225 Friction braking force 301 Switching unit 302 First limitation processing unit 303 Transient processing unit 304 Second limitation processing unit 305 Friction braking control unit 311 Operation determination unit 312 Hydraulic pressure control unit

Claims (6)

A regenerative braking force generator that generates regenerative braking force on the vehicle;
A battery for storing electric power regenerated by the regenerative braking force;
A friction braking force generator for generating friction braking force on the vehicle;
A control unit for controlling generation of the regenerative braking force and the friction braking force;
Have
The controller is
As a limit threshold of the regenerative braking force,
A first regeneration limit threshold set in accordance with the state of the battery;
A second regeneration limit threshold capable of generating a braking force greater than the first regeneration limit;
Have
In a state where regenerative braking is limited, a friction braking force is generated based on a difference between the second regenerative restriction threshold and the driver's required driving force,
When the friction braking force is further limited in the regenerative braking state, the limit threshold is switched from the second regeneration limit threshold to the first regeneration limit threshold.
The electric vehicle characterized by requesting the regenerative braking force generator to generate regenerative braking based on the first regenerative restriction threshold. The controller is
The electric vehicle according to claim 1, wherein when the driver performs an acceleration operation, the driver switches from the first regeneration restriction threshold value to the second regeneration restriction threshold value. The first regenerative restriction threshold value is based on a regenerative braking force that can be output by the regenerative braking force generation unit when the battery is in a regenerative braking state. Electric vehicle. The first regenerative restriction threshold value is based on a regenerative braking force that can be output by the regenerative braking force generation unit when the battery is in a non-regenerative braking state. The electric vehicle according to claim 1. The controller is
The electric vehicle according to any one of claims 1 to 4, wherein the regenerative braking generated based on the first regenerative restriction threshold value is smoothly output. The controller is
The electric vehicle according to any one of claims 1 to 5, wherein the friction braking force is gradually decreased when the friction braking is limited.

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